Solder-bearing lead

ABSTRACT

A solder-bearing lead for attachment to the surface of a substrate, wherein a discrete mass of solder is mechanically held firmly by the lead in a position permitting close proximity to the substrate surface to connect the lead to the substrate with an electrical and mechanical bond upon melting of the solder, the lead body having a pair of fingers partially encircling the solder mass with a gap between the fingers providing an unobstructed flow for the melted solder to the substrate. The lead may also be used to interconnect a first substrate to a second substrate, forming a bond between conductive areas on both substrates. 
     The present application is a continuation-in-part of application Ser. No. 416,505, filed Oct. 3, 1989, U.S. Pat. No. 5,052,954 which is a continuation of application Ser. No. 129,715, now U.S. Pat,. No. 4,883,435, and is also related to U.S. Pat. No. 4,728,305, U.S. Pat. No. 4,679,889, and U.S. Pat. No. 4,605,278. The disclosure of the parent application, Ser. No. 416,505 is incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a solder-bearing lead for attachment to asubstrate or integrated circuit chip or other circuit device, having adiscrete mass of solder mechanically held by the lead in position to bemelted for connecting the lead to the circuit device with both anelectrical and mechanical bond. The invention also relates to a dualsolder-bearing lead arrangement for attachment to an insulated holder,or substrate, and having a terminal pin arrangement for subsequentattachment to another substrate or a chip for connecting them to oneanother.

The lead of the present invention is of a type which is capable of beingcontinuously formed by a progressive stamping apparatus from a thinstrip of metal at high speed, and because each lead mechanically holdsits own discrete mass of solder, the leads may be produced individuallyor preferably are attached to a common carrier strip for automatedmachine insertion into mating receptacles in a substrate or holder orfor application to the surface of a substrate.

Various means have been previously provided where a quantity of solderis associated with a lead so that when the lead is juxtaposed to asubstrate (usually with a corresponding conductive surface area or padwith which the lead is to be connected), and the assembly is heated, themolten solder covers the juxtaposed surfaces of the lead and substrateto form, when cool, a soldered joint forming an electrical andmechanical connection between the lead and substrate.

In the prior art, in one form a solder mass or slug was associated witha lead by means of a metallurgical or mechanical bond between the solderand the lead, with the solder positioned with the lead between it andthe conductive area in the substrate. This method suffered frominconsistent solder bonds because the molten solder was required tomigrate to reach the junction between the lead and the region to whichthe lead was to be soldered.

In some arrangements the solder mass is held mechanically against thelead by various tabs or fingers, formed from the body of the lead. Thepresent invention constitutes an improvement on such arrangements.Examples of such other arrangements may be seen in U.S. Pat. Nos.4,120,558; 4,203,648; 4,592,617; 4,697,865; 4,728,305; 4,738,627;4,883,435; 4,932,876.

SUMMARY OF THE INVENTION

The present invention provides a simply formed lead arrangement whichsecurely holds a discrete mass of solder adjacent to a lead by means ofmechanical attachment. Two portions in the form of short fingers or tabsextending from the body of the lead wrap partially around the mass ofsolder, together holding it firmly in position. A gap provided betweenthe ends of these finger portions allows direct juxtaposition of themass of solder to a conductive area of a substrate.

It is thus an object of the present invention to provide improved meansand method for attaching securely a discrete solder mass to a lead in apurely mechanical manner.

It is a further object of the invention to provide a solder-bearing leadhaving its own supply of solder in a convenient location for forming abond with a substrate conductive area.

It is another object of the invention to provide a solder and leadassembly which can be made by very simple and efficient stamping steps.

It is yet another object to provide a unitary set of improvedsolder-bearing leads mounted on a holder or base permitting readysoldering to corresponding conductive areas of a substrate or circuitdevice, and also ready connection to a printed circuit board or thelike.

It is a still further object of the invention to provide certainimprovements in the form, construction and arrangement of the partswhereby these and other objects may be effectively attained. Theinvention accordingly comprises an article of manufacture possessing thefeatures, properties, and the relation of elements which will beexemplified in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Practical embodiments of the invention are shown in the accompanyingdrawings wherein;

FIG. 1 represents a front view of a partially processed blank forforming the leads of the invention during the manufacturing process;

FIG. 2 represents a front view of two leads according to the inventionattached to a conventional carrier strip;

FIG. 3 represents a side cross-sectional view of the lead shown in FIG.2 seen along line 3--3;

FIG. 4 represents a fragmentary perspective view of a part of a row ofleads according to the invention mounted on a lead holder;

FIG. 5 represents a top view of a portion of a holder showing, in smallscale, two parallel rows of receptacles for receiving terminal pinsforming part of the leads of the present invention;

FIG. 6 shows a cross-sectional view of a holder for two parallel rows ofleads according to the invention;

FIG. 7 shows a view as in FIG. 6 after soldering;

FIG. 8 represents a side and partial cross-sectional view of two leadsaccording to the invention mounted in opposing arrangement on a holderor substrate, with a second substrate positioned between the terminals;and

FIG. 9 represents a side and partial cross-sectional view of theassembly of FIG. 8 after the solder mass has melted and migrated to joinconductive areas of the two substrates.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 3, FIG. 1 shows a partially processed blank forthe present invention, formed from a continuous strip of slightlyresilient conductive material (e.g., beryllium copper or phosphorbronze) having one lateral edge 11 and a second edge at the position ofdashed line 13. That strip is stamped or punched to form individualleads 10 connected to a common carrier strip 12 as shown. The carrierstrip 12 may be provided with pilot holes 14 at regular intervals, as isconventional. The leads 10 are preferably spaced uniformly along strip11, with a pitch which matches holes or receptacles in a substrate orholder on which the leads are to be mounted; the pitch illustrativelymay be 0.100 inch. Each lead 10 includes a terminal pin 28 and a body18, with a top body section 16 joined to the carrier strip 12 and alower body section 20.

The central portion of body 18 is formed with a pair of U-shaped cuts 21with the open ends of the U cuts facing one another and leaving acentral area a between the U-cuts. Each U-cut then forms a short fingeror tab 22. Solder in the form of a wire or rod is then laid across theareas a as shown by dotted lines 23.

The carrier strip 12 may be any length desired, carrying a great numberof leads 10. The leads 10 and carrier strip 12 are preferably formed bycontinuously and progressively stamping them from a thin strip of metal.During the stamping operation, the fingers 22 are bent out of the planeof the body 18 of the lead 10 and are wrapped partially around thediscrete solder mass 24 to form the complete solder-bearing leads shownin FIGS. 2 and 3 (still integral with the carrier strip 12). During thestamping operation, when the free ends of the fingers 22 are wrappedaround the soft metal of the solder, the fingers 22 may be indented intothe surface of the solder to provide a firm mechanical attachmentbetween the solder and the lead 10, which prevents the solder frombecoming dislodged during shipping and handling, prior to the completionof the soldering operation. The fingers 22 do not completely surroundthe solder mass 24 but leave a gap 32 between the fingers 22 as seen inFIG. 3. The partially encircling engagement of the fingers 22 with thesolder 24 creates a firm grip on the solder 24 during the varioussubsequent assembly and handling operations.

The solder wire or rod may then be cut, as along lines 25, to leave asolder mass or slug 24 held on each lead 10 by its tabs 22. The lengthof the solder slug 24 is designed to provide the volume of solder neededfor a good soldered joint.

The body portion 18 also has a pair of small extensions or tabs 30, oneon each edge, which as described below serve to cause a compressive fitwith a hole or receptacle in a holder and may make contact with aconductive lining when provided in such a hole or receptacle.

In use, the terminal pin 28 of each lead 10 may be inserted into andsoldered to an adjacent circuit board, may have a wire or otherelectrical component soldered to it, may serve as a pin or bladeconnector of an electrical plug, may serve as a lead connecting tosockets or other circuit components, may have a wire or wiresconventionally wire-wrapped onto it, may function as a spring contact,or may have other electrical and mechanical connection whereappropriate. It will be understood also that the pins 28 may be made ascompliant pins, in the manner described in U.S. Pat. No. 4,932,876.

In one usage, each pin 28 is preferably of a size such as to permit itto pass into a receptacle 36 in a lead holder 38, shown in FIG. 6, withthe largest cross-sectional dimension of the receptacle no larger thanthe largest cross-section dimension of the lower body portion 20. Theprotuberances 30 provide a friction fit between each lead body and itsreceptacle, to hold the leads in place in the holder during subsequentoperations, such as insertion of the terminal pins 28 into correspondingreceptacles or holes of another substrate, or making connections to pins28. Where unnecessary or undesired, terminal pins 28 may be eliminatedentirely.

FIGS. 1 to 3 illustrate the leads 10 connected to a carrier strip 12.While this is a preferred embodiment suitable for automated machineinsertion of groups of leads into a holder or substrate, it is alsopossible, by virtue of the fact that each individual pin is firmlyattached to its own solder mass, to use the leads individually, as mightbe desired by the user of small quantities of leads. Also individualones or groups of leads 10 may be removed from the carrier strip 12without disturbing the remainder of the leads, to allow a customizedarray of leads to be inserted as a unit into a corresponding array 42 ofreceptacles 36 in a holder 38 as seen in FIG. 5.

FIGS. 6 and 7 show a side sectional view of a holder 38 carrying twoparallel rows of leads 10, two of which are shown in the figure. The twoleads 10 shown are representative of two rows of leads 10 that areinserted, for example, in the two rows 42 of receptacles 36 shown inFIG. 5.

It can be seen that the lower body portion 20 has been sized to fitclosely the receptacle 36 in the holder 38, while the tabs 30 extendingfrom the edge of the lower body portion 20 form a compressive fit withthe interior of the receptacle 36. When the leads are inserted into aninsulating holder 38, the tabs 30 maintain a compressive fit with theholder, while either the fingers 22 or terminal pins 28 or both areconnected to substrates or to other electronic components. It iscontemplated by the invention that an assembly consisting of a holder 38and a number of leads 10 could be soldered to one component at thefingers 22 and at a later time, another component could be soldered tothe pins 28. The reverse sequence may also be used.

A module or substrate 44, which is intended for connection to theterminal pins 28, may be inserted between the opposed pair of leads 10.The substrate 44 may be any component having at least one conductivearea or pad 46, such as an integrated circuit or chip carrier or printedcircuit board. As seen from FIG. 6, as well as FIG. 3, the pair offingers 22 leave an exposed portion 48 of the solder mass 24 at the gap32 between the ends of the two fingers 22, facing away from the lead 10.This exposed solder portion 48 may be placed in direct juxtapositionwith a corresponding conductive area 46 on the module substrate 44, asseen in FIG. 6. FIG. 7 shows a view similar to FIG. 6 after thesoldering of the contact pads 46 to the fingers 22. On heating, solderwill flow only around the fingers 22 and the conductive pad 46. Theholder, formed of an insulating material, will tend to repel solder.

As shown in FIGS. 8 and 9, instead of holder 38, a substrate 39 may besupplied having contact pads, each with or without a connectedconductive lining within the corresponding receptacle 36.

FIG. 8 shows a side sectional view of two leads 10 each inserted into areceptacle 36 in a substrate 39 which may be lined with a conductivecontact material 40 in the vicinity of the receptacle 36 and on itsinterior surface. The compressive fit formed by tabs 30 engaging lining40 contributes to good electrical contact between lead 10 and lining 40.

FIG. 8 also illustrates how the fingers 22 hold the solder 24 in closeproximity or juxtaposition to the lower body portion 20, the conductivearea 46, and the upper surface of the receptacle 36 prior to theapplication of heat and the completion of the soldering operation. Thelower finger 22 in this figure may be juxtaposed to or adjacent to theconductive area 45 of substrate 38.

FIG. 9 is a detailed view of the metallurgical joint formed between thelead 10, the conductive area 46, and the receptacle 36 after the lead 10and substrates 39,44 have been heating sufficiently to melt the solder24. It can be seen that the solder 24 may flow around the lower bodyportion 20, bonding together both the upper and the lower surfaceportions of the contact material 40 on the substrate 39, the interior ofthe receptacle 36, the fingers 22, and the conductive area 46. Thesolder mass 24 is formed of a sufficient amount of solder, such thatwhen the solder is heated and migrates to these various surfaces, thebond formed by the solder will be mechanically strong and electricallyconductive to all the above-mentioned surfaces.

One or both of the fingers 22 may also have a slit or slot 27, shown inFIG. 1, to permit the solder to flow more readily around the finger 22upon heating, to bond more firmly to the juxtaposed conductive area 46on cooling.

In FIG. 1, a slot 26 can be seen, formed in the lower body portion 20 bybending finger 22 out of the body portion 20 during the stampingoperation. The slot 26, the lower body portion 20 and the tabs 30 arecorrectly positioned and sized with respect to the thickness of theholder 38 or substrate 39 and the diameter of the receptacle 36 so thatthe body width at the tabs 30 is slightly over-sized with respect to thereceptacle 36 prior to insertion. The slot 26 permits the width of thebody portion to be resiliently compressed during insertion. Thisimproves the compressive fit and stability of the lead 10 within thereceptacle 36. As a result, a tight compressive fit is achieved afterinsertion, thereby making the lower part of lead 10 a compliant pin.This compliant pin portion produces a temporary mechanical bond betweenthe lead 10 and the receptacle 36 which allows additional handling ofthe electrical assembly such as the insertion of other electricalcomponents (e.g., a module substrate 44) or their testing prior tosoldering, without fear that the previously inserted leads will becomedislodged during such handling. The use of a compliant slot 26 incombination with tabs 30 to produce a compliant pin has additionaladvantages, including providing additional surface area in the lowerbody portion 20 for a better mechanical bond between the lower bodyportion 20 and the receptacle 36 and an improved electrical connectionwhen receptacle 36 has a conductive lining.

FIGS. 3 and 6 show that the two fingers 22 preferably do not cover theportion of the surface of the solder mass 24 most remote from the bodyof the lead 10, so that a line drawn tangent to the solder mass 24 atits distal end from the lead 10, parallel to the lead 10, will notintersect the fingers 22. This avoids blocking the solder from contactwith the conductive area 46 on the module substrate 44, which might leadto a diminished bond after solder melting and cooling. The leads 10 areat least slightly resilient, so that on insertion of substrate 44between the rows of leads 10, as in FIG. 6 or 8, upon heating to meltthe solder, the lead resiliency will urge the fingers 22 into contactwith the substrate conductive pads 46, to improve their electricalconnection. In practice, the solder mass 24 may be flush with thefingers 22. The gap 32 between the fingers 22 also allows a free flowroute for the molten solder after heating. The width of the fingers 22is also significantly smaller than the width of the solder mass 24,allowing molten solder to flow around the sides of the fingers 22 aswell.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above article without departingfrom the spirit and scope of the invention, it is intended that allmatter contained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. A solder-bearing lead for soldering to aconductive area of a substrate, comprising:an elongated body, and asolder mass, said body having two U-shaped cuts to define two fingers ina medial region of said body, each of said fingers having a first endintegral with and attached to said body at said medial region and alsohaving a free end, said first integral ends of said fingers beingsubstantially adjacent each other with said U-shaped cuts extending inopposite directions away from a predetermined position along said bodymedial region with the open ends of the cuts being on opposite sides ofsaid position and with said fingers extending in opposite directionsfrom said position, whereby the width of each finger may be formedindependently of the other, said fingers being bent out of the plane ofsaid body and each having a portion spaced from said body; said fingersencircling at least a portion of said solder mass, with a gap betweenthe free ends of said fingers, said solder mass being positioned againstsaid body at said position and remaining uncovered by said fingers atsaid gap, whereby, upon facing and directly juxtaposing said uncoveredsolder mass portion to said substrate conductive area and melting saidsolder, the solder is caused to flow unobstructedly into contact withsaid conductive area to solder said lead to said conductive area.
 2. Alead as in claim 1, wherein the proximal ends of said finger-likeportions are beneath said solder mass.
 3. A lead as in claim 2, whereinsaid proximal ends of said finger-like portions are adjacent theopposite side of said solder mass from said gap.
 4. A solder-bearinglead adapted to be held in a lead-receiving opening in a holder and tobe soldered to a conductive area on a substrate, said lead comprising:anelongated body having an upper body portion and a lower body portion,said lower body portion being sized to fit in said holder openingsubstantially perpendicular to said holder, said body having twoU-shaped cuts to define two fingers, each of said fingers having a firstend integral with and attached to said body and also having a free end,said first internal ends of said fingers being substantially adjacenteach other with said U-shaped cuts extending in opposite directions froma predetermined position along said body, said fingers being bent out ofthe plane of said body and each having a portion spaced from and inopposition to said body; a solder mass; said fingers being bent aroundsaid solder mass with said solder mass held between fingers, said fingerfree ends being wrapped only partially around said solder mass to leaveat least a portion of said solder mass uncovered by said fingers; saiduncovered solder mass portion being in a position to confront directlyand to contact said substrate conductive area with the free ends of saidfingers adjacent to said conductive area; and with one of said fingersbeing interposed between said solder mass and said holder.
 5. A lead asin claim 4, wherein said fingers are indented into the surface of themass of solder for holding the mass securely in position.
 6. A lead asin claim 4, wherein the lead has a lower terminal portion attached toand substantially axially aligned with the lower body portion, saidlower terminal portion being at least as small in its thickness andwidth as the lower body portion to allow the lower terminal portion topass through the opening in said holder.
 7. A lead as in claim 6,wherein said lower body portion has a protuberance at each edge designedto contact the inner wall of said holder opening.
 8. A method ofsoldering a lead to a conductive area of a substrate, comprising thesteps of:providing a solder-bearing lead as in claim 1; placing saidlead on aid substrate with said solder mass between said substrateconductive area and said body and with said substrate conductive areajuxtaposed to and directly confronting said uncovered solder mass andsaid fingers; and applying heat to melt said solder mass, whereby oncooling said lead is soldered to said conductive area.
 9. A method as inclaim 8 wherein each of said fingers is formed by a U-shaped cut in saidbody.
 10. A method as in claim 9 wherein said U-shaped cut issubstantially centrally of said body and between spaced lateral portionsof said body.
 11. A method of producing a lead for soldering to aconductive area of a substrate, comprising the steps of:forming aconductive elongated body, said body having two fingers extendingoppositely and longitudinally from a predetermined location along saidbody, each finger having a first end attached to said body at saidpredetermined location along said body, and each finger also having afree end spaced from said location; applying a solder mass against saidbody at said location; bending said fingers around said solder mass towrap them only partially around said solder mass with a portion of saidsolder mass uncovered between the free ends of said bent fingers;providing ah older, said holder having a plurality of receptacles, oneof said receptacles being dimensioned to receive and frictionally engagesaid lead; placing said lead within said one receptacle, such that saidlead will be immobile with respect to said holder.
 12. A method ofproducing an assembly of leads for soldering to conductive areas of asubstrate, comprising the steps of:providing a plurality of leads as inclaim 1; providing a holder, said holder having a plurality ofreceptacles, each of said receptacles being dimensioned to receive andfrictionally engage a respective one of said leads; and placing saidplurality of leads into said receptacles, such that said leads will beimmobile with respect to said holder.
 13. A method of producing a leadfor subsequent soldering to a conductive area of a substrate, comprisingthe steps of:forming a conductive elongated body, forming a U-shaped cutat one portion of said body to define a first finger having a first endintegral with and attached to said body at a position intermediate theends of said body and also having a free end, forming a second U-shapedcut on said body adjacent to but spaced longitudinally from saidposition and the open end of said second cut being on an opposite sideof said position from the open end of said first U-shaped cut, to definea second finger having a first end integral with and attached to saidbody and also having a free end, said U-shaped cuts extending inopposite directions away from said position, placing a solder mass onsaid body at said position, bending said fingers out of the plane ofsaid body around said solder mass to hold said solder mass between saidfingers, with said finger ends wrapped only partially around said soldermass to leave at least a portion of said solder mass uncovered by saidfingers, whereby said uncovered solder mass portion is in a position toconfront directly and to contact a substrate conductive area with thefree ends of said fingers adjacent to said conductive area.
 14. A methodas in claim 13, further comprising the steps of:heating said solder massto cause it to flow over said conductive area, and cooling said solderto solder said lead to said area.